The present invention relates to a method for mounting a bushing into a sheet metal member and also to a sheet metal member and bushing assembly. The present invention more particularly relates to a vehicle frame member and a method for making the same with a shock absorbing mounting portion.
One method of installing a bushing into a sheet metal member, such as a hydroformed tubular member, requires piercing or blanking a hole in a portion of the sheet metal member. The sheet metal member is then passed on to a secondary operation where the edge portion surrounding the pierced or blanked hole is extruded or drawformed to form an annular flange portion. A steel bushing is forced into the opening so as to form an interference fit between the annular flange portion and the bushing. A tight tolerance is required between the extruded drawformed annular flange portion and the bushing to provide the appropriate interference fit.
FIGS. 1A-3B illustrate conventional methods of installing a bushing in a hydroformed motor vehicle frame member. FIGS. 1A and 1B illustrate a punch 11 fastened to an upper moving ram of a reciprocating press, and an extrusion die 12 fixed to a lower stationary press bed. A tubular metal frame member which has been hydroformed from a seam-welded piece of sheet metal is partially shown and indicated at 100.
The extrusion die 12 is inserted in an open end of the hydroformed tubular member 100 and then lifted upwards to support the underside of an upper wall 10 of the member 100. The press ram then begins its downward stroke to force the punch 11 into contact with the metal material of the upper wall 10, as shown in FIG. 1A. When the press tonnage overcomes the tensile strength of the metal wall 10, the punch 11 shears the metal wall 10 against an opening 13 in die 12. The die opening 13 is defined at its upper end by a xe2x80x9chardxe2x80x9d or 90xc2x0 corner 35.
The scrap material or slug 15 passes through the die opening 13 and is eventually discarded, leaving hole 14 in the upper wall 10 of the tubular member 100. The diameter of the hole 14 corresponds to the outer diameter of punch 11. As shown in FIG. 1B, the press ram then starts its upward movement back to its starting position to move punch 11 away from the tubular member 100, and the tubular member 100 is then removed from the extrusion die 12. As a result of this hole forming operation, the edge portion surrounding the hole 14 will have a sharp, burred corner.
As shown in FIGS. 2A and 2B, after hole 14 is formed, the tubular member 100 is then moved to a drawforming station. At the drawforming station, a second die 20 is positioned inside the tubular member 100 and a press ram with a drawforming punch 16 is then cycled through a downstroke to locate a punch pilot 17 in alignment with the hole 14. The press ram then continues its downstroke to force a forming portion of the punch into engagement with the inner edge portion surrounding the hole 14. As shown in FIG. 2A, the press ram lowers the punch 16 lowers to a preset depth, so that the forming portion thereof draws the inner edge portion downwardly against a beveled upper edge 36 of the second die 20, thereby forming an annular drawformed flange portion 18. The press then begins its upstroke and removes upper punch 16 and punch pilot 17 from the tubular member 100. This causes the sharp, burred corner of annular flange portion 18 to be burnished smooth. As indicated by the arrow in FIG. 2B, the die 20 is then pulled out from the open end of the tubular frame member 100.
FIGS. 3A and 3B illustrate a steel can bushing 23 which has been pre-assembled in a separate operation from the punching operation. The tubular member 100 is placed in a holding fixture (not shown) that supports the underside of upper wall 10 close to the inner edge 25 of drawn flange 18. The bushing 23 is located directly above the hole 14 either manually or via the use of a machine. Downward pressure is applied to top surface 26 of the bushing 23 to force the busing through the hole 14 in the direction indicated by arrow 24. The pressure is then released and the finished assembly shown in FIG. 3B is produced with the bushing 23 being retained through an interference fit relation with the annular drawformed flange portion 18.
The problem with the above-described conventional method is that the fit between the exterior surface of the steel can bushing 23 and the annular drawformed flange portion 18 must be kept tight to ensure that the bushing 23 does not become separated from the tubular member 100. However, the fit must not be so tight that an extraordinarily high amount of effort is required to force the bushing 23 into the hole 14. Also, removal of the drawforming punch 16 burnishes the inner corner of the flange portion 18 which engages the bushing 23. As a result of this burnishing, the corner is smoother and does not xe2x80x9cbitexe2x80x9d into the bushing exterior to resist removal of the bushing.
It is therefore an object of the present invention to provide a sheet metal member with a bushing securely mounted therein which does not suffer the shortcomings of the construction described above. Specifically, it is an object of the present invention to ensure that the interference fit between the bushing and the sheet metal member is sufficient to prevent separation of the bushing from the member during normal vehicle operation. To achieve this object, one aspect of the present invention provides a method for mounting a bushing into a metal member which comprises providing a metal member forming a bushing receiving opening in the metal member, the opening defined by an annular edge portion surrounding the opening. A bushing is then forced through the opening in a bushing driving direction such that the bushing engages the annular edge portion and deforms the annular edge portion in the bushing driving direction to form an annular flange portion on the metal member which projects in the driving direction and engages an exterior surface of the bushing in an interference fit relation so as to securely retain the bushing within the opening.
In the method of the present invention, the need for a separate drawforming step, as in the above-described conventional method, is eliminated. The bushing itself acts as the drawforming tool as it is forced into the opening in the tubular member. Because the bushing acts as the drawforming tool, a tight interference fit between the annular wall portion and the bushing is ensured. Thus, the method of the present invention not only ensures a secure fit between the bushing and the tubular member, the method of the present invention also eliminates some of the tooling and operational steps of the conventional method.
Further, the corner of annular wall portion will not be burnished smooth because the drawforming tool (i.e., the bushing) is not withdrawn during the operation. An unburnished, burred, sharp corner is preferred because the sharp corner tends to xe2x80x9cbitexe2x80x9d into the exterior of the bushing when force is applied to the bushing in a direction opposite to the direction in which it was forced through the opening. Specifically, the annular flange portion will be drawn inwardly against the bushing as a result of such a force being applied to the bushing due to the sharp, burred corner being engaged with the bushing exterior.
This aspect of the present invention is more particularly related to a method for making a vehicle frame member with a shock absorbing mounting structure to be mounted to another structural component of a motor vehicle. The method comprises providing a tubular member surrounding a hollow interior and a lateral opening formed through the member. The member has an annular edge portion surrounding the opening. A shock absorbing mounting structure has a mounting portion constructed and arranged to be secured to the structural component of the motor vehicle and a yieldable shock absorbing portion associated with the mounting portion. The shock absorbing mounting structure is forced inwardly through the opening such that the mounting structure engages the annular edge portion and deforms the annular edge portion inwardly into the hollow interior of the tubular member to form an annular flange portion that engages an exterior surface of the mounting structure in an interference fit relation so as to securely retain the mounting structure within the opening, thereby enabling the tubular member to be resiliently mounted to the aforesaid structural component. Further, a portion of the second opposing surface adjacent the opening is supported while the mounting structure is being forced through the opening such that only the annular edge portion is substantially deformed by the mounting structure.
Another aspect of the present invention provides a metal member and bushing assembly comprising: a metal member having a bushing receiving opening formed therethrough and an annular flange portion surrounding the opening and projecting from the metal member in a bushing driving direction. A bushing is securely mounted inside the bushing receiving opening with the annular flange portion engaging the bushing in an interference fit relation as a result of the bushing being forced through the bushing receiving opening in the bushing driving direction such that the bushing engages an annular edge portion surrounding the opening and deforms the annular edge portion in the driving direction to form the annular flange portion.
It can be appreciated that a sheet metal member and bushing assembly constructed according to the principles of this aspect of the invention has a secure fit between the bushing and the sheet metal member. Failures due to varying tolerances between the bushing and the sheet metal member can be substantially eliminated because the bushing acts as the punch tool itself.
This aspect of the present invention is more particularly concerned with a vehicle frame member to be mounted to a structural component within a motor vehicle. The frame member comprises a tubular member surrounding a hollow interior. The tubular member has a lateral opening formed therethrough and an annular flange portion which surrounds the opening and projects inwardly into the hollow interior from the mounting portion. A shock absorbing mounting structure is securely mounted within the opening with the annular flange portion tightly engaging the mounting structure in an interference fit relation as a result of the mounting structure being forced inwardly through the opening such that the mounting structure engages an annular edge portion of the tubular member surrounding the opening and deforms the annular edge portion inwardly toward the hollow interior to form the annular flange portion. The mounting structure has a mounting portion constructed and arranged to be secured to the aforesaid structural component of the motor vehicle and a yieldable shock absorbing portion associated with the mounting portion. The mounting portion is constructed and arranged to enable the mounting structure to be resiliently mounted to the structural component. The shock absorbing portion permits relative movement between the mounting portion and the tubular wall to provide for limited relative movement between the tubular member and the structural component.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.